Tube tapering roller chuck



March 11, 1969 c. F. KENNEDY E AL TUBE TAPERING ROLLER CHUCK Filed March 10, 1967 INVENTOR5. /FFOIQD F. KENNEDY THOMAS M 5/ /54 70 mum 28 Ill!!!" u E V I March 11, 1969 c. F. KENNEDY ET AL 3,431,764 I Filed March 10, 1967 W 5. UL? AGE/V7 Sheet 3 of 4 INVENTORS- F'A EN/VEDV M. SHEA 7' ON CL/FFOPD THOMAS March 11, 1969 c. KENNEDY E wusz mama ROLLER cnucx Filed March 10, 1967 March 1969 c. F. KENNEDY ET AL 3,431,764

TUBE TAPERING ROLLER CHUCK Filed March 10, 1967 Sheet 4 of 4 v 26 w F/L55a 6a F F/5.55 28 PM 27 ,4 7- rae/ve' Y United States Patent 3,431,764 TUBE TAPERING ROLLER CHUCK Clifford F. Kennedy, Simi, and Thomas M. Shelton, Glendale, Califi, assignors to North American Rockwell Corporation, a corporation of Delaware Filed Mar. 10, 1967, Ser. No. 622,168

US. Cl. 7278 14 Claims Int. Cl. B21tl 3/00, 3/04; B21b 19/02 ABSTRACT OF THE DISCLOSURE Apparatus for tapering the walls of tubes being drawn under constant tension through a plurality of adjustable roller dies whose axes are inclined to the tube axis. The dies have concavely contoured peripheries that make spiral line contact with the tube periphery during tapering.

CROSS REFERENCES TO RELATED APPLICATIONS The present invention is an improvement of the invention disclosed in US. application Ser. No. 458,553, now Patent No. 3,363,442 issued Jan. 16, 1968, entitled, Tube Tapering Device, filed May 25, 1965, by the same inventors of the present invention and which application has been assigned to the same assignee of this invention. This invention is also related to the invention disclosed in US. application 469,088, now abandoned, entitled, Tube Tapering Device, filed on July 2, 1965, by Roderick K. Johns and which application has been assigned to the same assignee of this invention.

BACKGROUND OF THE INVENTION This invention relates to tapering the walls of workpieces having circular cross sections and more specifically it relates to a process and apparatus for tapering tubular walls with a plurality of adjustable roller dies. The general concept of tapering or symmetrically deforming the walls of tubes is known in the tube tapering art as illustrated in US. Patent 2,432,566 to Findlater. When the roller dies lie perpendicularly across the tube axis, as is the most common practice, the resulting circular line contact made by the dies on the tube periphery makes the tube prone to buckling and crushing. To avoid this serious problem it is customary to dispose mandrels inside the tube which is both costly and limiting on the range of tapering that can be accomplished. US. Patent 1,782,968 to Keller teaches a similar arrangement for tapering tubes wherein the roller dies taper by exerting uniaxial force upon the tube.

To make the tube more amenable to deformation it should be placed in tension. While in most cases the tensile forces exerted on the tube depend upon the speed at which the tube is pulled through a series of draw dies, more sophisticated arrangements have been developed. However, none are capable of exerting a constant tension. When tension is variable and unpredictable cracking and tearing of the tube cannot be easily eliminated and therefore to assure tapering under safety conditions the draw speed must be diminished. Such penalty in tapering speed can be a severe restriction. The use of dies with contoured surfaces as shown in US. Patent 3,240,045 to Sellars et al., which make area contact with the tube being tapered suffers from inherent slow draw speeds due to the resulting intense frictional contact. This arrangement also makes the tube prone to tearing and excessive ductility or catastrophic necking down because of extreme loads exerted in the tailstock vicinity. As pointed out in the above mentioned US. application Ser. No. 458,553, a plurality of adjustable roller dies can be aligned with their axes across the axis of the tubular workpiece. However, these roller dies have cylindrical exterior peripheries posing a number of disadvantages eliminated by the instant invention as shall be more fully described below.

SUMMARY OF THE INVENTION Briefly described, this invention comprehends a chuck assembly mounting a plurality of equiangularly spaced roller dies that are simutlaneously adjustable for continuously tapering the walls of a tubular workpiece. The dies are connected to the chuck so that their axes assume a fixed inclination relative to the tube axis, preferably between 35 and 55. The peripheral portions of the dies that make rolling engagement with the tube are concavely contoured so that they make helical line contact with the tube. When the dies and tube are rotated relative to one another, this arrangement achieves a uniform load distribution along the helical contact line and a minimal torque so that buckling and longitudinal collapse of the tube are substantially minimized. As the tube is being drawn into shape it is subjected to a constant tensile force by a device that exerts a pulling force on the nontapered end of the tube.

In another aspect, this invention comprehends the procedure of disposing a plurality of concavely contoured roller dies across the axis of the tube at an inclination of between 35 and 55. During relative rotation between the roller dies and the tube, helical line contact is achieved between them.

The above indicated and other advantages of this invention will be fully appreciated upon studying the following detailed description in conjunction with the detailed drawings in which:

FIG. 1 is a schematic view of a lathe assembly incorporating the chuck and roller die assembly of this invention;

FIG. 2 is a perspective view of the chuck and roller die assembly of this invention with portions cut away to show how spiral line contact is accomplished between the roller dies and tube being tapered;

FIG. 3 is a plan view showing the relative angulation between a single roller die and the tube being tapered;

FIG. 4 is a perspective view of a section of the tube that has been tapered and illustrates a path of spiral line contact;

FIG. 5 is a perspective and partly exploded view of one chuck assembly that may incorporate this invention, a portion of the chuck assembly being cut away to show details thereof.

FIG. 6 is an exploded view of components of the chuck assembly shown in FIG. 5;

FIG. 7 is a perspective and exploded view of an alternative chuck assembly;

FIG. 8 is a longitudinal cross section of a tube section that has been tapered;

FIG. 8a is a cross sectional end view of a tapered portion of the tube taken along line 8a of FIG. 8;

FIG. 8b is a cross sectional end view of a nontapered portion of the tube taken along line 8b of FIG. 8;

FIG. 9 is a schematic view showing a system for applying a constant tensile force on the tube being tapered.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 'Referring now to the drawings in detail, FIG. 1 schematically illustrates a lathe assembly 10 with which the instant invention can be used. Lathe assembly 10 includes a typical lathe bed 12 formed with guideways 13 on which a chuck carriage 16 rides. Canriage 16 can be driven along the guideways 13 by any suitable device such as a conventional lead screw (not shown) operated by a variable feed rate motor (not shown). Rigidly mounted on carriage 16 is a draw chuck assembly 20 that mounts a plurality of roller die blocks 24. The particular structural relationship between chuck 20 and roller die blocks 24 constitutes one aspect of the instant invention as will be more fully described below. Passing through the center of chuck 20 is an elongated tube 26 that is to be tapered. Draw chuck 20 moves parallel to the axis of tube 26 in a direction indicated by the arrow T which signifies the tapering direction.

During tapering, the rearward end 28 of tube 26 is held stationary While the forward end 27 is connected to a movable tension applying device 29 to be more fully described below. The tension applying device 29 pulls on end 27 as tube 26 continuously grows or elongates during tapering so that a constant uniaxial tensile force will be exerted throughout tube 26. As draw chuck assembly 20 traverses tube 26 in tapering direction T from tapered end 28 to nontapered end 27, it is rotating relative to tube 26 which is restrained from rotation.

In order to control the desired tapering pattern of tube 26, a conventional template 30 is provided which dictates the tapering movements of roller die blocks 24. Template 30 acting as a cam surface is engaged by a stylus 32 that serves as a cam follower by tracing over the cam surface of template 30. Stylus 32 is connected to a standard balanced tracer valve 34 which communicates by way of fluid lines 36 and 37 with a tracer cylinder 40. Stylus 32 is spring-biased so that it always seeks smooth engagement with template 30. In response to fluid selectively pumped through lines 36 or 37 to the opposite faces of a piston head 41, an associated tracer piston rod 42 imparts longitudinal movement to a slide frame 44. A typical linkage 35 functions to coordinate movement of tracer piston rod 42 with tracer valve 34. Slide frame 44 is mounted on carriage 16 for relative movement therewith and includes a transverse arm 45. Arm 45 is rigidly secured to a collar 47 in turn connected through a suitable ball thrust bearing (not shown) to an actuator tube 48 designed to rotate with draw chuck assembly 20. Fore and aft movement of actuator tube 48, as will be more fully explained below, operates roller die blocks 24 causing them to simultaneously move toward or away from tube 26.

Many of the components of lathe and the mechanism for controlling the movements of draw chuck assembly 20 are available on the commercial market so that a detailed explanation of them is not necessary to fully appreciate this invention. In the preferred embodiment chosen to illustrate this invention, draw chuck 20 rotates around and is fed longitudinally along the axis of tube 26. However, by slight modifications there would be no departure from this invention if the tube 26 were mounted in headstock and tailstock portions (not shown) of lathe 10 and rotatably pulled longitudinally through a stationary chuck assembly. So long as there is relative longitudinal and rotational movement between tube 26 and chuck assembly 20, the benefits of this invention can be realized.

Referring now to FIG. 2, chuck assembly 20 and its associated roller die blocks 24 are shown removed from the other portions of lathe assembly 10. Chuck 20 has a generally circular housing 50 with a centrally hollowed space 51. Tube 26 is aligned coaxially with space 51, as well as with actuator tube 48. Formed in housing 50 are three equiangularly spaced and radially extending slots or guideways 52. Die blocks 24 are disposed in guideways 52 and are confined to radial sliding movement therein by T sections 56 that are received by complementary T- shaped portions of guideways 52. During tapering chuck assembly 20 is fed in tapering direction T as blocks 24 are simultaneously moved inwardly or outwardly relative to tube 26.

Secured to inner ends 68 of the three roller blocks 24 are pairs of retaining arms 69. Extending between each pair-of arms 69 is a roller die 70 journalled at its opposite ends on arms 69 by way or conventional roller bearing assemblies 72. Roller dies 70 are identically contoured, polished very smooth and may be constructed from graphite molybdenum steel. When tube tapering is to be done in cryogenic environments the roller dies 70 can be constructed of tungsten carbide. The particular metal or alloy used forms no part of this invention.

An important aspect of this invention concerns the relative angulation 6, as shown in FIG. 3, between the axes of roller dies 70 and the longitudinal axis of tube 26. As shall be pointed out, as long as the relative angulation 6 is within a range permitting helical line contact between the peripheries of roller dies 70 and the tube being tapered, then unexpected and superior tapering results are achieved. FIG. 3 shows a portion of a single roller die 70 with its axis crossing the axis of tube 26. During tapering roller die 70 is revolved around tube 26 while being fed forwardly in direction T so as to push against and deform the transition-deformation portion 26d, of tube 26. Roller die 70 has an enlarged leading end 70b and a narrower trailing end 70a separated by a central portion 70c. Central portion 70c is generally concave and smoothly merges with slightly convexed shoulder 70s adjacent end 7 0b. Roller die 70 could alternatively be hour-glass shaped in which case both ends 'would be enlarged relative to a constricted central portion. The contouring of roller die 70 is designed so that helical line contact will be made between it and tube 26. Helical line contact in the transition-deformation zone 26d as shown in FIG. 4 is represented by letter H.

When relative angulation 9 is less than 20 the tube becomes unstable and prone to buckling. For some purposes this may be beneficial; for example, when polysided spiral tubes are desired for ornamentation. It has been discovered that optimum tube tapering results are achieved when relative angulation 6 is in a range of between 35 and 55. In this range, helical line contact H, shown in FIG. 4, is optimum and is characterized by a compound curve. By way of analogy it is well known that the end domes of an egg will support greater direct force than will the side Walls of the egg. A force that would crush an egg if applied to its side walls would not collapse the egg if applied to the dome ends. This same phenomenon exists with respect to the deformation forces applied to the wall of tube 26 by roller dies 70. As the relative angulation 0 decreases below 35 the spiral line contact tends to become straight line contact, thereby making the tube more prone to collapse. During the transition it is as though the force applied to the egg has shifted from the domes to the egg side walls. By way of contrast as the relative angulation 0 is increased from 35, helical line contact becomes more compound or pronounced at least through a range with its maximum limit at around 55.

When the relative angulation 0 is 35 or less, roller dies 76 tend to cause the tube to become polysided. Also sliding friction in this range becomes increased so that the tube walls are prone to surface cracks and tearing. The resulting approximate straight line force distribution in this range facilitates tube buckling. However, if the relative angulation 0 is too great, in excess of 55, then the roller chuck exerts a great pulling force on the tapered portion 28 of tube 26. This produces greatly increased tensile stress that can result in catastrophic necking down because the ultimate yield stress of the tube material is exceeded. In addition, as the relative angulation 6 is increased, beyond 55", the force from the roller dies tends to become concentrated point forces capable of crushing tube 26. In accordance with the instant invention, these foregoing potentially destructive conditions are substantially eliminated because of the compound helical line contact made between the roller dies 70' and tube 26. Under these conditions minimum torque exists between the roller dies 70 and tube 26, thereby minimizing burnishing, rubbing, and work-hardening that can eventually cause cracks in the tubes surface. By minimizing workhardening, a superior polished finish is achieved and a thinner tube wall can be obtained. Maximum draw speed is achieved when relative angulation 0 is between 35 and 55. This is obtainable because of virtual forces equalization on tube 26.

Shown in FIG. 5 is an embodiment of a specific draw chuck assembly 20 with a quarter section removed so that important components can be illustrated. Selective longitudinal motion of actuator tube 48 is transmitted through three pivotally mounted actuator cams 71 that impart simultaneous radial motion to roller die blocks 24, only one of which is shown. Actuator cams 71 are mounted to interior wall portions of a chuck housing section 50 that can be detachably connected to remaining portions (not shown) of the chuck housing by bolt connectors 53.

As shown in FIG. 6 the forward end of actuator tube 48 is formed with an enlarged head 80 that has three equidistantly spaced and transversely extending cam slots 82. Each actuator cam 71 has a rounded inner edge 74 positioned in a corresponding cam slot 82 and an outer edge 76 positioned in a corresponding cam slot 84 formed in a jaw portion 54 of block 24. Cant 71 is pivotally connected within chuck housing 50 (shown in FIG. 5) by *way of a transversely extending fulcrum pin 72. Each pin 72 is seated in a hole (not shown) drilled in housing 50, the hole being perpendicular to a radial line in housing section '50. It can now be seen that when actuator tube 48 is driven forwardly, i.e., in a direction towards roller dies 71, cam inner edge 74 will be pivoted forwardly as cam outer edge 76 is driven upwardly. The upward movement of cam outer edge 76 slides its associated jaw 54 in a radial outward direction. Thus the roller dies 70 (shown in FIG. 2) will become spaced further apart so as to produce a taper of increased diameter. Conversely, rearward motion of actuator tube 48 will pivot earns 71 in an opposite direction causing cam outer edges 76' to slide their jaws 54 radially inwardly. In the resulting position, roller dies 70 produce a tapered Wall of relatively smaller diameter.

An alternative embodiment of a draw chuck assembly 20 is shown in FIG. 7. A cam shoe 80 of general frustoconical shape has a central opening 82 through which the tubular workpiece (not shown) is disposed while being tapered. Shoe 80 may be connected to actuator tube 48 by bolts 83 extending between retaining apertures 86 of shoe 80 and apertures 87 of a flange 89 attached to actuator tube 48. Three identical equally spaced cam slots 84 are formed in shoe 80 and have T-shaped cross sections that define sloped slide ramps 85. Attached to each roller block jaw portion 54 is a cam element 92 having a T-shaped cam section 94 designed to be retained in sliding relationship in T-shaped cam slot 84. Forward motion of actuator tube 48 drives cam shoe 80 forwardly forcing ramp 85 to slide against cam section 94. This action forces jaw 54 to slide in a radially outward direction. When cam actuator 48 is retracted, then simultaneous inward movement of jaws 54 is produced due to the sliding action of cam surfaces 96 of jaw 54 and overhanging cam surfaces 88 of shoe 80. Those skilled in the chuck assembly and tube tapering art would recognize numerous other suitable chuck designs for accomplishing simultaneous movement of roller dies 70'.

In order to facilitate the tube tapering operation and make the tubular workpiece more amenable to deformation, the instant invention contemplates applying a pretension fore to the workpiece 26. Conventional arrangements for applying tension loads to a tube by static weights are satisfactory for some applications. However, these arrangements are incapable of applying constant tension to the tube. When the tube is subjected to variable or unpredicatable forces the tube becomes prone to cracking. Tension applying device 29 shown in FIG. 1 is designed to apply a predetermined constant tensile force to the tube 26. In practice, tube 26 is preloaded to a predetermined tensile force slightly in excess of the yield stress or elastic limit of the metal from which tube 26 is constructed. Above this level the strain produced becomes permanent and assumes its deformed shape when the load is released.

Referring to FIG. 8, a longitudinal section of tube 26 is shown. FIGS. 8a and 8b respectively, .show cross sections of tapered portion 28 and nontapered portion 27. When tube 26 is maintained in tension then ideally A2 SY2=A1 Where:

A =Cross sectional area of undrawn tube portion 27 A =Cross section area of drawn tube portion 28 SY =Stress slightly above the yield point of undrawn tube portion 27 SY =Stress below the ultimate yield point of drawn tube portion 28.

When a force equal to A SY is greater than the force of A SY then the wall portion of tube 26 being tapered will be thinner than if these two forces were equivalent. Conversely, if a force constituted by A SY is less than the force of A SY than a Wall portion of tube 26 being tapered would be relatively thicker than if the forces were equivalent. These different tapering conditions can be regulated by adjusting the relative angulation 0, (referring to FIG. 3). As previously mentioned, when angle 0 is increased from 55 to there is a concomitant increase in torque between the chuck assembly and tube 26. The resulting increased load on tapered tube portion 28 will then produce relative thinning in the wall portions of tube 26 being tapered. If the increased tensile load in tapered portion 28 exceeds the ultimate yield stress catastrophic necking down will result. It should be pointed out that the more workhardened a metal becomes the higher its ultimate yield stress becomes. Some metals such as Inconel X are very fast work-hardening materials whereas 304 stainless steel is a slow work-hardening material. Thus the more workhardened a metal becomes, the more increased load it can absorb without exceeding its ultimate yield stress. These facts are taken into consideration in practicing the instant invention.

With slight modification this invention can be used when the metal from which tube 26 is constructed is at optimum ductility at higher or lower temperatures than ambient temperature. For example, titanium has poor ductility at ambient temperature and work hardens very fast so thatit becomes prone to cracking under relative small forces. This invention could be applied to the titanium tube by heating it by a suitable resistance heating technique to between 400 and 800 F. As a result, the ductility of the tube would be approximately doubled. In a similar manner, when a metal increases in ductility at lower than ambient temperatures such as 304 stainless steel, cryogenic fluid could be conducted through the tube 26.

Referring now to FIG. 9, a specific embodiment of a tension applying device 29 is schematically shown. The nontapered end 27 of tube 26 is clamped in a clamping chuck 104. Chuck 104 is connected to a slidable support 106 that is connected to a piston rod 110 associated with a hydraulic cylinder 112. Attached to piston rod 110 is a conventional piston head 111 that slides in cylinder 112 that is divided into variable fluid chambers 114 and 115. Cylinder 112 is controlled by a pumping assembly incorporating twin positive displacement pumps 144 and 145 housed in a canister 141. Pump assembly 140 functions to supply pressurized fluid from a reservoir 142 into cylinder 112 to maintain a constant differential pressure between chambers 114 and 115. The differential pressure is used to keep a constant pulling force on tube 26 under its static and dynamic conditions.

At all times during tube tapering, piston 110 pulls on tube 26 to automatically compensate for its axial lengthening. As tube 26 axially grows or elongates, piston rod 110 experiences variable strain that is sensed by a strain gage SG attached thereto. Strain gage SG is represented by variable resistor R; that is electrically hooked-up in a Wheatstone bridge circuit WB. Before the tapering operation commences, variable resistor R is fixed at a preselected value that corresponds to the desired tensile force to be exerted on tube 26. Preferably the stress should slightly exceed the yield point of the material from which tube 26 is construced. Lengthening of tube 26 pushes rod 110 displacing fluid in chamber 114 while increasing its pressure. Concomitantly the pressure in chamber 115 is reduced and a diminished strain results in strain gage SG. The tension on tube 26 is thus diminished below the desired value. The resulting change in electrical resistance reflected resistor R causes the balance of Wheatstone bridge WB to become upset. To restore the desired tension in tube 26, Wheatstone bridge WB must be rebalanced.

-Pump assembly 140 functions to rebalance Wheatstone bridge WB. To achieve this result pump 144 includes a meshed gear set 146 and 147 and pump 145 similarly includes a meshed gear set 148 and 149. The individual gears rotate in directions indicated by the arrows. A pump cavity 151 is shaped so that the clearance between the individual gears and the surrounding wall defined by cavity 151 permits the existence of a labyrinth seal. By this arrangement pressurized fluid is trapped between successive teeth of the individual gears and conveyed upwardly into conduits 155 and 157. Fluid enters cavity 151 through ports 151 and 153 that are in communications with reservoir 142. Conduit 155 is in communication with chamber 114 and conduit 157 is in communication with chamber 115.

Movement of fluid through conduits 155 and 157 is controlled by a solenoid 120 actuated by electrical power supplied from the Wheatstone bridge WB when it is unbalanced. Solenoid 120 has a solenoid spool 1121 interconnected by a fulcrum assembly 122 to a dual balance valve assembly 124. Assembly 124 has a valve 129 which is for closing communication between conduit 155 and reservoir 142 and a valve 128 which similarly can close communication between conduit 157 and reservoir 142'.

During pauses in the tapering operation Wheatstone bridge WB will be balanced. The solenoid spool 121 will be in its neutral position and therefore valves 128 and 129 will be equally opened. The pressure differential in cylinder 112 will then be constant. However, Wheatstone bridge \VB is unbalanced, indicating that tension in tube 26 has become less than the predetermined tensile value, solenoid spool 121 will be moved to the right. This action will simultaneously close valve 128 while opening valve 129 so that the pressure in line 155 is decreased while the pressure in line 157 is increased. At this time valve 129 acts as a bypass valve so that fluid is exhausted from line 155 back into reservoir 142. When the fluid pressure in chamber 115 has been increased to a point where the previous pressure differential between chambers 115 and 114 is reestablished, then concomitantly the strain in strain gage SG, will be at a value sufficient to rebalance Wheatstone bridge WB. Solenoid spool 121 will then shift to the left so that valves 128 and 129 will become identically situated.

This cycle of action is continuously repeated in system 29 during tapering so as to automatically compensate for axial lengthening of tube 26. Thus for every increment of axial growth by tube 26 which pushes rod 110 to the left, strain is caused in strain gage 86 that unbalances Wheatstone bridge WB. In turn, solenoid assembly 120 operates valve assembly 124 to actuate pump assembly 140 which restores the necessary pressure differential in cylinder 112 to compensate for the increment by which tube 26 has become axially lengthened.

It should be pointed out that pump assembly 140 is stationary and that the bore length of cylinder 112 is always greater than the predetermined distance by which tube 26 will elongate. Assuming that the roller dies are oriented so that the wall thickness of tube 26 remains constant before and after tapering, rod .110 always moves at a rate dictated by the percentage by which the diameter of tube 26 is decreased. For example, if a 40 percent diameter reduction is being made in tube 26, then rod would be moving at a rate as fast as the chuck assembly draw speed. Thus if the draw speed is 35 inches per minute then rod 110 would be retreating at a rate of 14 inches per minute.

The foregoing embodiments that have been described in detail were chosen for the purpose of best illustrating the instant invention. After understanding this invention, those skilled in the art will be aware of alternative embodiments for achieving the benefits of this invention. The scope of this invention is intended to be limited only by the scope of the following claims.

What is claimed is:

1. In a tube tapering device comprising a draw chuck having a plurality of jaws, a plurality of radially oriented roller dies connected to the jaws, means for adjustably opening and closing the roller dies relative to a tubular workpiece surrounded by the roller dies, and means for causing relative rotational and longitudinal movement between the chuck and the tubular workpiece during tapering, the improvement wherein:

the roller dies are concavely contoured with their longitudinal axes disposed to cross the tubular workpiece longitudinal axis so that during tube tapering the dies will engage the workpiece in spiral line contact.

2. The structure according to claim 1 wherein the included angle between said roller die axes and said tubular workpiece axis is from 35 to 55.

3. The structure according to claim 1 wherein the roller dies are equiangularly spaced and are three in number.

4. The structure according to claim 1 further comprising means for applying a constant predetermined tensile force on the tubular workpiece as it is being tapered.

5. The structure according to claim 4 wherein the means for applying a constant tensile force comprises a strain sensitive element that senses lengthening in the tubular workpiece being tapered, and, means responsive to the strain sensitive element for automatically compensating for the lengthening.

6. The structure according to claim 5 wherein the means responsive to the strain sensitive element comprises a fluid cylinder having a piston rod connected to the tubular workpiece for pulling the workpiece.

7. The structure according to claim '6 wherein the strain sensitive element is a strain gage electrically connected in a Wheatstone bridge circuit which when unbalanced actuates the piston rod to restore constant tension in the tubular workpiece.

8. The structure according to claim 1 wherein the means for adjustably moving the roller dies includes an actuator tube which is connected to the chuck and in which the tubular workpiece is disposed.

9. The structure according to claim 8 wherein the chuck comprises:

a cam shoe of frusto-conical shape connected to the actuator tube, the shoe being formed with a plurality of sloped cam slots, cam elements connected to the jaws which are retained in sliding engagement in the cam slots,

whereby axial movement of the actuator tube causes movement of the roller dies relative to the tubular workpiece.

10. The structure according to claim 9 wherein the cam slots and the cam elements have complementary T-shaped cross sections.

-11. The structure according to claim 8 wherein the chuck comprises a plurality of actuator cams formed with inner and outer cam edges, the cams being pivotally mounted to the chuck, and cam slots formed in the actuator tube and jaws to receive the inner and outer cam edges respectively.

12. In a tube tapering device comprising a draw chuck having a plurality of jaws, a plurality of radially oriented roller dies connected to the jaws, means for adjustably opening and closing the roller dies relative to a tubular workpiece surrounded by the roller dies, and means for causing relative rotational and longitudinal movement between the chuck and the tubular workpiece during tapering, the improvement wherein:

the roller dies are concavely contoured with their longitudinal axes angularly disposed to the tubular Workpiece longitudinal axis so that during tube tapering the dies will engage the tubular workpiece in spiral line contact, and

means is provided for applying a constant predetermined tensile force on the tubular workpiece as it its being tapered.

13. The structure according to claim ,12 wherein said roller die axes are disposed across said tube axis at an angle of from 35 to 55 and,

the means for applying a constant tensile force comprises a strain sensitive element that senses lengthening in the tubular workpiece being tapered and means responsive to the strain sensitive element for automatically compensating for the lengthening.

14. A process of tapering a tube with a draw chuck having a plurality of adjustable, radially oriented roller dies that have concavely contoured peripheries comprising the steps of:

disposing the roller dies with their axis crossing the tube axis at between and engaging the roller dies and tube in spiral line contact and causing relative radial, rotational and longitudinal movement of the roller dies and tube to taper the tube.

References Cited UNITED STATES PATENTS 331,582 12/1885 Tasker 72-100 1,782,968 11/1930 Keller 72-224 2,432,566 12/ 1947 Findlater 72-209 3,240,045 3/ 1966 Sellars et a1 72-2O5 RICHARD J. HERBST, Primary Examiner.

US. Cl. X.R. 

